All images are astrometrically calibrated. For each of the 2116 mean fields, we provide the following:

  1. Instrumental: fields where the FITS data is in counts. These fields include the MAGZP header keyword, to convert instrument magnitudes to calibrated magnitudes.
  2. Photometrically Calibrated: photometrically calibrated fields, in that the FITS data is offsetted with the above-mentioned zero-point and converted to Janskies.
  3. Star-Removed: starless fields, where the FITS data was offsetted with the above-mentioned zero-point before star-removal processes were run and converted to Janskies.
  4. Individual Exposures: the individual exposures comprising the stack. The number of exposures ranges - background levels vary throughout the night, and we occassionaly exclude exposures with outlying backgrounds to enhance the quality of our mean-combined stack. With a future release version, each field will have exactly 12 quality-verified individual exposures.

Photometric Calibration

The instrumental images include the MAGZP keyword in their FITS headers. This represents the magnitude zero-point for each field image and can be used to calculate calibrated AB magnitudes, mag(MDW), from measured instrumental flux, as such:

mag(MDW) = -2.5*log10(measured flux [counts]) + MAGZP

The magnitude zero-point for each field is calculated by comparing the instrumental Hα magnitudes of sources in each field with the catalog-matched IGAPS' AB Hα magnitudes. We specifically try to offset our data such that the stellar locus of our color-color plots align with the IGAPS synthetic early-A reddening line.

For the photometrically calibrated and photometrically calibrated star-removed field images, we convert the MAGZP value into a physical flux zero-point and apply it to the FITS data unit. In this way, the measured values (e.g. in aperture photometry) result in a calibrated AB Hα magnitude. Note that the FITS data has the unit of Janskies.

mag(MDW) = -2.5*log10(measured flux [Jy] / 3631 [Jy])

Download Images

Note: as the initial release, some fields might have less files than others. These will be updated as we actively take extra exposures.